266 research outputs found
Miniature cyclotron resonance ion source using small permanent magnet
An ion source using the cyclotron resonance principle is described. A miniaturized ion source device is used in an air gap of a small permanent magnet with a substantially uniform field in the air gap of about 0.5 inch. The device and permanent magnet are placed in an enclosure which is maintained at a high vacuum (typically 10 to the minus 7th power) into which a sample gas can be introduced. The ion beam end of the device is placed very close to an aperture through which an ion beam can exit into the apparatus for an experiment
Measurements of the dielectric constants for planetary volatiles
The model of Titan at present has the surface temperature, pressure, and composition such that there is a possibility of a binary ethane-methane ocean. Proposed experiments for future Titan flybys include microwave mappers. Very little has been measured of the dielectric properties of the small hydrocarbons at these radar frequencies. An experiment was conducted utilizing a slotted line to measure the dielectric properties of the hydrocarbons, methane to heptane, from room temperature to -180 C. Measurements of the real part of the dielectric constants are accurate to + or - 0.006 and the imaginary part (the loss tangent) of the liquids studied is less than or equal to 0.001. In order to verify this low loss tangent, the real part of the dielectric constant of hexane at 25 C was studied as a function of the frequency range of the slotted line system used. The dielectric constant of hexane at room temperature, between 500 MHz and 3 MHz, is constant within experimental error
Getting a Grip on the Transverse Motion in a Zeeman Decelerator
Zeeman deceleration is an experimental technique in which inhomogeneous,
time-dependent magnetic fields generated inside an array of solenoid coils are
used to manipulate the velocity of a supersonic beam. A 12-stage Zeeman
decelerator has been built and characterized using hydrogen atoms as a test
system. The instrument has several original features including the possibility
to replace each deceleration coil individually. In this article, we give a
detailed description of the experimental setup, and illustrate its performance.
We demonstrate that the overall acceptance in a Zeeman decelerator can be
significantly increased with only minor changes to the setup itself. This is
achieved by applying a rather low, anti-parallel magnetic field in one of the
solenoid coils that forms a temporally varying quadrupole field, and improves
particle confinement in the transverse direction. The results are reproduced by
three-dimensional numerical particle trajectory simulations thus allowing for a
rigorous analysis of the experimental data. The findings suggest the use of a
modified coil configuration to improve transverse focusing during the
deceleration process.Comment: accepted by J. Chem. Phy
Ion-Molecule Reactions in Unsaturated Hydrocarbons: Allene, Propyne, Diacetylene, and Vinylacetylene
Ion-molecule reactions in allene, propyne, diacetylene, and vinylacetylene (1-buten-3-yne) have been studied at near-thermal energies by the technique of ion cyclotron resonance mass spectrometry. Rate coefficients and branching ratios are reported for the reactions of C_3H^+_n (n = 1-4) with allene and propyne and for the reactions of C_4H^+_n (n = 0-5) with diacetylene and vinylacetylene. Branching ratios are also given for the reactions of C_4H^+_n, C_5H_n, and C_6H^+_n with propyne and for reactions of C_6H^+_n with diacetylene and vinylacetylene. More than 90% of the reactive channels lead to product ions having a larger carbon skeleton than the reactant ion. Evidence for ions with the same m/e ratio having differing reactivities was obtained for C_3H^+_3, C_6H^+_7, and C_7H^+_7. Ion reaction sequences in allene and propyne were followed at higher pressures (l0^(-4) torr) to investigate secondary, tertiary, and higher order processes
Radial Distribution of Production Rates, Loss Rates and Densities Corresponding to Ion Masses <=40 amu in the Inner Coma of Comet Halley: Composition and Chemistry
In this paper we have studied the chemistry of C, H, N, O, and S compounds
corresponding to ions of masses <=40 amu in the inner coma of the comet
1P/Halley. The production rates, loss rates, and ion mass densities are
calculated using the Analytical Yield Spectrum approach and solving coupled
continuity equation controlled by the steady state photochemical equilibrium
condition. The primary ionization sources in the model are solar EUV photons,
photoelectrons, and auroral electrons of the solar wind origin. The chemical
model couples ion-neutral, electron-neutral, photon-neutral and electron-ion
reactions among ions, neutrals, electrons, and photons through over 600
chemical reactions. Of the 46 ions considered in the model the chemistry of 24
important ions are discussed in this paper. The calculated ion mass densities
are compared with the Giotto Ion Mass Spectrometer (IMS) and Neutral Mass
Spectrometer (NMS) data at radial distances 1500, 3500, and 6000 km.Comment: pages 42, figures 9 (total 12), tables
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The Psychological Experience of Middle-Power in Social Hierarchies: A Theoretical and Empirical Investigation
In this dissertation, I theoretically and empirically examine the psychological experience of middle-power, which occurs when someone frequently alternates between adopting behavioral strategies targeting higher-power and lower-power interaction partners. In Chapter 1, I update and extend the approach/inhibition theory of power (Keltner, Gruenfeld, & Anderson, 2003) by developing a novel theoretical framework related to the psychological experience of middle-power. This new theoretical perspective draws from and integrates insights from role-based identity (Ashforth & Johnson, 2001; Stryker, 1980) and role transition theories (Ashforth, Kreiner, & Fugate, 2000). In Chapter 2, I conduct a systematic review of the social hierarchy literature over the past 10 years and demonstrate that scholars have considered the middle of the distribution with respect to stratifying variables in only 5.4% of past empirical investigations. This conscious absence of the middle forces us to reconsider existing findings in the social hierarchy literature. In Chapters 3 and 4, I examine the relationship between power and unethical behavior and present evidence of a curvilinear relationship: middle-power individuals consistently behave more ethically than both their higher and lower-power counterparts. Taken together, these insights highlight the importance of considering the antecedents and consequences of middle-power states
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